Aliens attack Earth. You need to build up defenses to protect humanity. After that you invade aliens homeworld.
This game is a mix of RTS and TD genres. You have the command center which you must protect. Enemies come from everywhere. You can build refineries to gather resources and place towers.
It's like a usual RTS game but you don't make units but towers. Could be really nice, but it is not. First campaign contains 10 levels. All these levels looks like the same, I have got only 2 towers (actually 1 tower and better version of it) and 3 enemies (alien, big alien, bigger alien). It was like I played same level 10 times. Almost nothing changes.
Do you think second campaign is better? No... i have got totally new tower only at 16 mission. Yeah, missions are short but anyway. it's not fun. Also I played on hard and I am sure i could beat then by playing only 1 toe.
Between missions you make research which unlocks new stuff. And it's the best part of the game. It's cool. But it's not enough to make the game good, because it's not the main gameplay.